1. Field of the Invention
The invention relates to a sponge cloth made of cellulose and a process for producing same.
2. Description of Related Art
The publication Ullmann's Encyklopadie der technischen Chemie [Encyclopedia of Industrial Chemistry], 3.sup.rd edition (1967) vol. 18, pp. 175-177, describes a process for producing a spongy cellulose structure where layers of pulp obtained from wood are swollen in a 15-20% NaOH solution that is present in excess. Sodium cellulose is formed after a period of time. The sodium hydroxide solution is then squeezed out; it contains dissolved hemicelluloses that would otherwise interfere with the subsequent process steps. The remaining pressed cake in ground form is treated with carbon disulfide, forming cellulose xanthogenate, which dissolves readily in a NaOH solution, in which it degrades after a period of time with a reduction in average degree of polymerization (DP). Depending on the grade of pulp used and the storage time, the DP is reduced from 800-1200 to 200-600.
The DP is defined as the average number of individual cellulose molecules of which a cellulose polymer chain is composed on the average.
The alkaline xanthogenate solution is then mixed with pore-forming Glauber's salt, cotton fibers and optionally a coloring pigment and the mixture is stirred or kneaded until all the components are distributed uniformly. Then the mixture is spread on a web by means of a flat device or a roller-like device. The web may have a three-dimensional pattern for profiling the surface of the product.
The mass on the web is guided for a few minutes in an alkaline coagulation bath enriched with Glauber's salt at 100 C. The xanthogenate is thermally cleaved and the pore-forming salt is leached out, forming a spongy structure as the sheet product on the web. The sheet product is washed in water and brought in contact with a small amount of 1% sulfuric acid solution to reduce the residual levels of organic carbon disulfide and hydrogen sulfide compounds.